The treadmill test--where to stop and what does it mean?

The prognostic utility of an exercise ECG test depends upon having an adequate workload to stress the cardiac system. A negative stress test, in which there are no adverse clinical or ECG findings, and in which an adequate workload is achieved, stratifies patients into a low-risk group. The 1997 American Heart Association guidelines imply that any index of workload--heart rate, rate-pressure product, or exercise duration in multiples of resting O2 consumption (METS)--could be used to indicate that adequate stress was achieved. However, while there is considerable evidence supporting the use of METS as a strong independent prognostic variable, there is less support for the use of rate-pressure product or heart rate. Indeed, there is evidence that a high heart rate at a low workload carries an adverse prognosis. Further research is needed to identify the number of METS achieved that would define an adequate workload. In the meantime, a review of the literature suggests that 7 to 10 METS is a reasonable ballpark figure of the minimum workload in patients with a negative stress test that would imply a favorable outcome.